1. Field of the Invention
The invention is a semiconductor sensor with pixel structure, containing a capacity for each pixel which stores charge and converts it into voltage that can be read out. The pixel structure is in the main completely covered with a conductive layer. Furthermore the invention is about the sensor's use integrated in a vacuum system (IC) with photo cathode. The semiconductor is ideal for image processing in opto-electronic applications.
2. Prior Art
Opto-electronic image converters are known in semiconductor technology. With the so-called CCD-device electrons are removed from the lattice structure by the incidence of photons on the sensor surface, which are then stored in so-called pixel cells at the conversion place and can be read out afterwards in different ways. Moreover active-pixel-sensors (APS) are known, where each pixel is connected with at least one transistor that converts or decouples the pixel information for direct read out at inquiry.
A disadvantage, however, is that the known image converters react sensible against electrons that striking the sensor surface. The kinetic energy of the electrons influences the crystalline semiconductor structure, so that the system is forced open under operation with the result of pixel defects, which show for example in dark currents. Therefore it does not make sense to integrate such a semiconductor element into an image intensifier tube, to, for example, convert the information directly into a video signal.
A pixel structure covered by a conductive layer is known from the EP 0 588 397 A2 in the form of an x-ray image detector. The conductive layer serves as a pre-voltage electrode, in order to lead charges that are generated in a photo conductor layer, under influence of a by this electrode produced electric field, to each individual gathering electrode of the pixels. Similar semiconductor image sensors are known for example from the EP 0 444 702 A1, the patent abstract of Japan JP 06310699 A, 1994, JPO, the U.S. Pat. No. 4,789,888 and the U.S. Pat. No. 5,311,038 in the form of light- and/or x-ray sensible sensors. From the two last-mentioned files it is known in addition to cover gaps, in order to avoid the unwelcome influence of incident light.
From the U.S. Pat. No. 3,902,095 an electron beam semiconductor intensifier with shielded diode junctions is known, which is designed as electron beam semiconductor tube, for example as transmitter amplifier, switching tube or as driving circuit for other high-voltage intensifier tubes, like for example traveling-wave power tubes for radar transmitters. The semiconductor is partially covered with a conductive coating, the shielding having openings above a segment of the diode junction. Here the electrons are to strike well-aimed, the screening preventing unwelcome electron bombardment in the periphery areas of the device (diode). By this unwelcome surface- and bulk charging effects are eliminated. Therefore the maximum reverse bias voltage is increased and hence the maximum possible output power of tubes employing such diodes is increased, too. The interconnection of a plurality of such diodes causes an increase of the intensifier's efficiency, the capacitance being reduced in proportion to the exposed surface. Nevertheless the semiconductor tube is neither designed nor suited for an image transmitting detection.
Moreover from the patent abstracts of Japan: JP 2-94566 A E-944, 1990, Vol. 14/No. 292 a semiconductor with pixel electrodes with a further, at least gap-covering layer is known. But this is an optical semiconductor sensor, at which multiple reflections on the inside of the optical covering (layer are reduced or eliminated by a reflection avoiding film.
Besides, from the DE 42 23 693 A1 an x-ray image intensifier together with a vacuum housing, an input illumination screen, an electron optic and an image sensor, which is located on the side of the vacuum housing that is opposite to the input illumination screen, is known, where the from a photo cathode resulting electrons are converted directly into a video signal in a CCD-image converter. At this, the image sensor contains a layer system, which has at least one semiconductor layer that initiates an electron conversion and is of amorphous semiconductor material. This publication therefore shows a concrete different solution of the following problem.